Studies with bilingual and multilingual subjects suggest that bilingualism and multilingualism foster the development of certain aspects of children’s metalinguistic skills. The purpose of the present study was to find out if learning foreign languages facilitates children’s metalinguistic ability to define words. It compared Bulgarian monolingual, bilingual and trilingual subjects on their word-definition performance in the L1. The relationship between L1 definition performance, L2/L3 proficiency, and L2/L3 definition performance within the bilingual and trilingual groups was also investigated. The study found that early foreign language education has a positive effect on the quality of children’s definitions in their L1. The bilingual and trilingual children performed significantly better than the monolingual children. The results specific to the bilingual and trilingual groups showed that second/third language proficiency was a significant and powerful predictor of the performance of the bilingual and trilingual subjects on the word-definition tasks in their second/third language. L1 word-definition ability was a weaker predictor of the subjects’ performance on the word-definition task in their second or third language. However, in the case of genetically closely related languages (Bulgarian and Russian) the transfer was easier as compared to genetically more distanced languages (Bulgarian and English).